The earth comprises a biosphere in which microorganisms, plants, and animals, including humans, exist in a more-or-less steady state.
It is desirable to provide a microcosm of the biosphere known as earth to study the interaction of components and for development of techniques for influencing our environment. Such experiments are difficult at best in the open system provided on earth, since matter is exchanged between the earth's environment and the experiment. It is therefore desirable to provide a system that is completely enclosed, so that no matter is exchanged with the earth's environment.
Currently, a completely closed ecological system, referred to as Biosphere 2, is being established near Oracle, Arizona. The system completely encloses about one hectare of land and 175,000 cubic meters of space, isolated from the earth's environment by an impermeable skin so that no matter is transferred.
In an attempt to completely simulate the environs of earth, a saltwater "ocean" and an estuary have been included in Biosphere 2. The estuary is fed, upstream from fresh-water ponds and at a downstream point, by saltwater pumped from the ocean. This low-salinity water simulates tidal marshlands, which are fresh-water near their source but are of increasing salinity toward their ocean outlets. The Biosphere 2 marshlands provide a suitable ecosystem for the growth of numerous organisms which result in an accumulation of organic materials which build up in the marshlands environment. This organic material can provide a source of nutrition for organisms in the saltwater ocean.
To disperse the nutrients, a tide is simulated. High tide in the ocean is low tide in the marsh, and vice versa, as water is caused to flow back and forth between these biomes. After high tide, resulting from the gradual accumulation of water pumped into the marshlands, the water is allowed to flow from the marshlands to the ocean, thus providing nutrients to the ocean organisms. When low tide is reached, the water level is again allowed to rise in the marshlands, which allows the accumulation of more organic material and nutrients. In addition to providing nutrients to the ocean life, the tides also provide a suitable ecosystem for the growth of the tidal organisms of the marshlands which require the cyclical high and low tides for their survival.
The method for tide creation in the oceans and estuaries of the world is through the gravitational influence of the moon. In Biosphere 2, the lunar influence is minimal, and the ocean and estuary tides must be simulated by manmade means.